The invention relates to a method for applying a detectable reference mark on a rotating body to be balanced, said mark being of a character to generate a reference signal used (1) for measuring the unbalance position and (2) for positioning the body during unbalance correction.
In the measurement of an unbalance in accordance with conventionval practices, the body to be balanced is rotated at an unbalance measuring rotary speed. While being so rotated the force or displacement oscillation of the body are measured in its bearings. The phase of the force or displacement oscillations permits determination of the position of the unbalance on the body, and thus of those locations in which mass must be removed or added by an appropriate unbalance correction apparatus. The phase of the force or displacement oscillations is measured in relation to a reference signal. This reference signal corresponds to a certain point of the rotating body in relation to which the angular position of the unbalance on the body to be balanced is determined. The present invention relates to the establishment of a reference mark on the body to produce such a reference signal.
In many cases the body to be balanced rotates freely during the unbalance measuring procedure without being connected to a drive motor. Then a reference signal for determining the unbalance position is generated by applying a reference mark on the body to be balanced and by detecting said mark without contacting the body. The position of the unbalance is then determined by the angular position of the unbalance with respect to the reference mark.
It is known to apply on the body to be balanced a reference mark in the form of a contrast color dot or dash, which may then be detected photoelectrically. Furthermore, photoelectric methods are known with which an axial groove or bore is provided on the rotating body. A light beam passes through this groove in a certain angular position and impinges upon a photoelectric detector. Furthermore, magnetic or inductive methods are known, wherein an element present on the rotating body or provided for this purpose by the design of the body, and interrupting the contour of the body, for example a groove or a key inserted into such groove, is detected. The marks detected photoelectrically, magnetically or inductively provide one short-time pulse per revolution. This pulse is converted into an electric signal of sinusoidal, triangular or rectangular waveform in a signal generator or processing circuit, this signal having a fixed phase relation with respect to the pulse. The reference signal thus obtained, which represents an instantaneous angular position of the rotating body about its rotational axis, is processed in an unbalance signal processing circuit together with the signals derived from the force or displacement oscillations. The unbalance signal processing circuit provides output signals which represent the angular position of the unbalance relative to the reference mark, and the amount of the unbalance.
In manufacturing operations the application of photoelectrically detectable marks presents problems, in particular with balancing in quantity production, in which short balancing times are essential. The reference marks are mostly applied manually as a dot of paint, which is time consuming and usually not too accurate. Higher accuracy can be achieved by affixing adhesive tape of light reflecting material. The application of such adhesive tape, however, requires still more time. Experiments to apply the reference marks mechanically have not yet led to satisfactory results. The photoelectric detection of grooves or bores of the rotating body as well as the magnetic or inductive detection is limited to individual cases, where the design permits such measures.
In order to avoid the problems described in the field of the automatic balancing of electromotors in series, a method is known wherein the contour of the motor rotor interrupted by the slots is scanned. Thus a twelvefold slotted motor rotor generates twelve pulses per revolution which, for example, are applied to a counter counting from 1 to 12. One of these twelve individual pulses is declared to be the reference pulse, i.e., the reference mark, to which the unbalance measurement is referred. When the body is braked down, the electric counting system remains coupled thereto. During a positioning procedure following the braking down, the body is controlled angularly by the counting system such that the land of the interrupted contour generating the reference pulse comes to a standstill in a certain angular position. An appropriate gripping and conveying device conveys the body from this position into the subsequent correcting station and places it thus positioned into this correcting station. A further rotating procedure in the correcting station takes care of the body being adjusted to the correct correction position opposite the correcting tool, on the basis of the stored measuring data for the unbalance position with respect to the prepositioned reference land.
This method suffers from the disadvantage that its application is limited to bodies having multiple interrupted contours, preferably to slotted bodies. Furthermore, as a rule, it can be used only if measuring and correcting stations and interlinked with each other. It is not possible to remove the body in any optional way from the measuring station, as at this moment its angular reference would be lost. This is disadvantageous in particular with semi-automatic balancing installations. The method is appropriate, with the limitation to bodies having interrupted contours, substantially to fully automatic installations, the economic use of which is restricted to mass production.
The present invention permits automatic application of a detectable reference mark on an annular ferromagnetic portion of a body to be balanced, and without physical contact being made with the body.
The method of the invention is characterized by the following procedural steps: magnetic homogenization of a ferromagnetic rotating track of the body; generating a short-time magnetic pulse of high intensity at a location immediately adjacent the rotating track to produce a locally limited, permanent magnetization serving as said reference mark.
The invention also relates to an apparatus for the carrying out of the method.